Grand Unification Scale Research Articles

Grand unification in high-scale supersymmetry

A constraint on masses of superheavy gauge and Higgs multiplets at the grand unification (GUT) scale is obtained from the gauge coupling unification in the case of high-scale supersymmetry. We found that all of the particles may lie around a scale of 1016 GeV so that the threshold corrections to the gauge coupling constants at the GUT scale are smaller than those in the case of the low-energy supersymmetry. In addition, the GUT scale tends to be slightly lower when the gauginos are heavier and, thus, the proton decay rate via the X-boson exchange process is expected to be enhanced.

The Hyper-Kamiokande project

The Hyper-Kamiokande, which we are currently developing, is designed to be the next decadeʼs flagship experiment for the study of neutrino oscillations, nucleon decays, and astrophysical neutrinos. The detector is the third generation underground water Cherenkov detector at Kamioka. Holding 1 million ton water target being about 20 times larger than the Super-Kamiokande, the detector will extend the sensitivity to search for baryon-number-violated proton (and bound neutron) decays by one order of magnitude or more to test various grand unified theories. It also aims to explore the full picture of neutrino masses and mixings by using intense accelerator and atmospheric neutrinos. These experimental studies would become windows to see physics at the grand unification scale of ∼1016GeV which is far beyond the energy scale of accelerator based particle physics. The detector also serves as an astrophysical neutrino observatory aiming to study the explosion mechanism of core-collapse supernova, the history of star formation and heavy element synthesis in the universe, WIMP dark matters trapped in the Sun, Earth, and Galaxy, and other astrophysical neutrino sources.Physics potential of the Hyper-Kamiokande is estimated based on the well proven water Cherenkov technology and its detector performance. Feasibility of the one megaton size detector has been shown by its baseline design, and the detector design is being optimized at present. By taking into account the production rate of photo-sensors and estimated construction period, the Hyper-Kamiokande is expected to start its operation in 2023.

Unification of gauge couplings in the standard model with extra vectorlike families

We discuss gauge coupling unification in models with additional one to four complete vectorlike families and derive simple rules for masses of vectorlike fermions required for exact gauge coupling unification. These mass rules and the classification scheme are generalized to an arbitrary extension of the standard model. We focus on scenarios with three or more vectorlike families in which the values of gauge couplings at the electroweak scale are highly insensitive to the grand unification scale, the unified gauge coupling, and the masses of vectorlike fermions. Their observed values can be mostly understood from infrared fixed-point behavior. With respect to sensitivity to fundamental parameters, the model with three extra vectorlike families stands out. It requires vectorlike fermions with masses of order 1--100 TeV, and thus at least part of the spectrum may be within the reach of the LHC. The constraints on proton lifetime can be easily satisfied in these models since the best motivated grand unification scale is at $\ensuremath{\sim}{10}^{16}\text{ }\text{ }\mathrm{GeV}$. The Higgs quartic coupling remains positive all the way to the grand unification scale, and thus the electroweak minimum of the Higgs potential is stable.

Yukawa unification predictions for the LHC

This paper is divided into two parts. In the first part we analyze the consequences, for the LHC, of gauge and third-family Yukawa coupling unification with a particular set of boundary conditions defined at the grand unification scale. We perform a global ${\ensuremath{\chi}}^{2}$ analysis including the observables ${M}_{W}$, ${M}_{Z}$, ${G}_{F}$, ${\ensuremath{\alpha}}_{\mathrm{em}}^{\ensuremath{-}1}$, ${\ensuremath{\alpha}}_{s}({M}_{Z})$, ${M}_{t}$, ${m}_{b}({m}_{b})$, ${M}_{\ensuremath{\tau}}$, $\mathrm{BR}(B\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma})$, $\mathrm{BR}({B}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})$, and ${M}_{h}$. The fit is performed in the minimal supersymmetric Standard Model in terms of nine grand unification-scale parameters, while $\mathrm{tan}\ensuremath{\beta}$ and $\ensuremath{\mu}$ are fixed at the weak scale. Good fits suggest an upper bound on the gluino mass, ${M}_{\stackrel{\texttildelow{}}{g}}\ensuremath{\lesssim}2\text{ }\text{ }\mathrm{TeV}$. This constraint comes predominantly from fitting the bottom-quark and Higgs masses (assuming a 125 GeV Higgs). Gluinos should be visible at the LHC in the 14 TeV run but they cannot be described by the typical simplified models. This is because the branching ratios for $\stackrel{\texttildelow{}}{g}\ensuremath{\rightarrow}t\overline{t}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1,2}^{0}$, $b\overline{b}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1,2}^{0}$, $t\overline{b}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1,2}^{\ensuremath{-}}$, $b\overline{t}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1,2}^{+}$, $g{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1,2,3,4}^{0}$ are comparable. Top squarks and sbottoms may also be visible. Charginos and neutralinos can be light, with the lightest supersymmetric particle predominantly bino-like. In the second part of the paper we analyze a complete three-family model and discuss the quality of the global ${\ensuremath{\chi}}^{2}$ fits and the differences between the third-family analysis and the full three-family analysis for overlapping observables. We note that the light Higgs in our model couples to matter like the Standard Model Higgs. Any deviation from this would rule out this model.

Higgs mass via type II seesaw mechanism

We show that the simplest supersymmetric scenario where a large Higgs mass can be attained at tree level for any ratio of the Higgs vacuum expectation values corresponds to the case where the neutrino masses are generated through the type II seesaw mechanism. This allows a standard model-like Higgs with mass around 125 GeV without assuming a heavy spectrum for the top squarks. We show that our results are consistent with the bounds coming from perturbativity up to the grand unified scale and discuss gauge coupling unification and possible signals at the Large Hadron Collider.

SEARCHING FOR LIGHT WEAKLY INTERACTING MASSIVE PARTICLES AT THE LARGE HADRON COLLIDER

Light neutralinos implemented in an effective Minimal Supersymmetric extension of the Standard Model at the electroweak scale without requirement of a gaugino-mass unification at a grand unification scale may have a mass around 10 GeV, i.e. in the range of interest for present data of direct search for dark matter particles in the galactic halo. In this talk we discuss the challenges and prospects of searching for them at the Large Hadron Collider.

Correlated curvature perturbations and magnetogenesis from the GUT gauge bosons

In the context of hybrid inflation at the scale of grand unification, it is shown that, if (some of) the gauge bosons of the unbroken grand unified group obtain a flat superhorizon spectrum of perturbations from inflation they can affect or even generate the observed curvature perturbation and simultaneously produce a sizable primordial magnetic field capable of explaining galactic magnetism. The mechanism employs the vector curvaton idea for a supermassive grand unified gauge boson after the breaking of grand unification.

130 GeV Fermi gamma-ray line from dark matter decay

The 130 GeV gamma-ray line based on tentative analyses on the Fermi-LAT data is hard to be understood with dark matter annihilation in the conventional framework of the MSSM. We point out that it can be nicely explained with two body decay of a scalar dark matter (ϕ˜DM→γγ) by the dimension 6 operator suppressed with the mass of the grand unification scale (∼1016GeV), L⊃|ϕ˜DM|2FμνFμν/MGUT2, in which the scalar dark matter ϕ˜DM develops a TeV scale vacuum expectation value. We propose a viable model explaining the 130 GeV gamma-ray line.

Probing the stability of superheavy dark matter particles with high-energy neutrinos

Two of the most fundamental properties of the dark matter particle, the mass and the lifetime, are only weakly constrained by the astronomical and cosmological evidence of dark matter. We derive in this paper lower limits on the lifetime of dark matter particles with masses in the range 10TeV−1015TeV from the non-observation of ultrahigh energy neutrinos in the AMANDA, IceCube, Auger and ANITA experiments. For dark matter particles which produce neutrinos in a two body or a three body leptonic decay, we find that the dark matter lifetime must be longer than \U0001d4aa(1026−1028)s for masses between 10 TeV and the Grand Unification scale. Finally, we also calculate, for concrete particle physics scenarios, the limits on the strength of the interactions that induce the dark matter decay.

Could two NMSSM Higgs bosons be present near 125 GeV?

We examine next-to-minimal supersymmetric model scenarios with partial parameter unification at the grand unification scale in which both ${h}_{1}$ and ${h}_{2}$ lie in the 123--128 GeV mass range. Very substantially enhanced $\ensuremath{\gamma}\ensuremath{\gamma}$ and other rates are possible. Broadened mass peaks are natural.

Implications of gauge kinetic mixing onZ′and slepton production at the LHC

We consider a supersymmetric version of the standard model extended by an additional $U(1{)}_{B\ensuremath{-}L}$. This model can be embedded in an mSUGRA-inspired model where the mass parameters of the scalars and gauginos unify at the scale of grand unification. In this class of models the renormalization group equation evolution of gauge couplings as well as of the soft SUSY-breaking parameters require the proper treatment of gauge kinetic mixing. We first show that this has a profound impact on the phenomenolgy of the ${Z}^{\ensuremath{'}}$ and as a consequence the current LHC bounds on its mass are reduced significantly from about 1970 GeV to 1790 GeV. They are even further reduced if the ${Z}^{\ensuremath{'}}$ can decay into supersymmetric particles. Secondly, we show that in this way sleptons can be produced at the LHC in the 14 TeV phase with masses of several hundred GeV. In the case of squark and gluino masses in the multi-TeV range, this might become an important discovery channel for sleptons up to 800 GeV (900 GeV) for an integrated luminosity of $100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ ($300\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$).

Composite inflation setup and glueball inflation

We explore the paradigm in which inflation is driven by a four-dimensional strongly coupled dynamic with a nonminimal coupling to gravity. We introduce a model where the inflaton is identified with the glueball field of a pure Yang-Mills theory. We introduce the dilatonic-like glueball action, which is obtained by requiring saturation of the underlying Yang-Mills trace anomaly at the effective action level. We couple the resulting action nonminimally to gravity. We demonstrate that it is possible to achieve successful inflation with the confining scale of the underlying Yang-Mills theory naturally of the order of the grand unified energy scale. We also argue that the metric formulation gives a more consistent picture for models of composite inflation than the Palatini one. Finally, we show that, within the metric formulation, the model nicely respects tree-level unitarity for the scattering of the inflaton field all the way to the Planck scale.

Yukawa coupling unification inSO(10)with positiveμand a heavier gluino

The $t\mathrm{\text{\ensuremath{-}}}b\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ unification with positive Higgs mass parameter $\ensuremath{\mu}$ in the minimal supersymmetric standard model prefers ``just so'' Higgs splitting and a light gluino $\ensuremath{\lesssim}500\text{ }\text{ }\mathrm{GeV}$ which appears to be ruled out by the recent LHC searches. We reanalyze constraints on soft supersymmetry breaking parameters in this scenario, allowing independent splittings among squarks and Higgs doublets at the grand unification scale, and show that it is possible to obtain $t\mathrm{\text{\ensuremath{-}}}b\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ unification and satisfy experimental constraints on gluino mass without raising supersymmetry breaking scale to very high value $\ensuremath{\sim}20\text{ }\text{ }\mathrm{TeV}$. We discuss the origin of independent squark and Higgs splittings in realistic $SO(10)$ models. Just so Higgs splitting can be induced without significantly affecting the $t\mathrm{\text{\ensuremath{-}}}b\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ unification in $SO(10)$ models containing Higgs fields transforming as $10+\overline{126}+126+210$. This splitting arises in the presence of nonuniversal boundary conditions from mixing between 10 and other Higgs fields. Similarly, if additional matter fields are introduced then their mixing with the matter multiplet 16 is shown to generate the squark splitting required to raise the gluino mass within the $t\mathrm{\text{\ensuremath{-}}}b\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ unified models with positive $\ensuremath{\mu}$.

Postcards from oases in the desert: phenomenology of SUSY with intermediate scales

The presence of new matter fields charged under the Standard Model gauge group at intermediate scales below the Grand Unification scale modifies the renormalization group evolution of the gauge couplings. This can in turn significantly change the running of the Minimal Supersymmetric Standard Model parameters, in particular the gaugino and the scalar masses. In the absence of new large Yukawa couplings we can parameterise all the intermediate scale models in terms of only two parameters controlling the size of the unified gauge coupling. As a consequence of the modified running, the low energy spectrum can be strongly affected with interesting phenomenological consequences. In particular, we show that scalar over gaugino mass ratios tend to increase and the regions of the parameter space with neutralino Dark Matter compatible with cosmological observations get drastically modified. Moreover, we discuss some observables that can be used to test the intermediate scale physics at the LHC in a wide class of models.

Heavy and light scalar leptoquarks in proton decay

We list scalar leptoquarks that mediate proton decay via renormalizable couplings to the Standard Model fermions. We employ a general basis of baryon number violating operators to parameterize contributions of each leptoquark towards proton decay. This then sets the stage for investigation of bounds on the leptoquark couplings to fermions with respect to the most current Super Kamiokande results on proton stability. We quantify if, and when, it is necessary to have leptoquark masses close to a scale of grand unification in the realistic SU(5) and flipped SU(5) frameworks. The most and the least conservative lower bounds on the leptoquark masses are then presented. We furthermore single out a leptoquark without phenomenologically dangerous tree-level exchanges that might explain discrepancy of the forward-backward asymmetries in $t \bar t$ production observed at Tevatron, if relatively light. The same state could also play significant role in explaining muon anomalous magnetic moment. We identify contributions of this leptoquark to dimension-six operators, mediated through a box diagram, and tree-level dimension-nine operators, that would destabilize proton if sizable leptoquark and diquark couplings were to be simultaneously present.

Insensitive unification of gauge couplings

The standard model extended by three vector-like families with masses of order 1 TeV–100 TeV allows for unification of gauge couplings. The values of gauge couplings at the electroweak scale are highly insensitive to fundamental parameters. The grand unification scale is large enough to avoid the problem with fast proton decay. The electroweak minimum of the Higgs potential is stable.

Spontaneous [formula omitted] breaking as the origin of the hot early universe

The decay of a false vacuum of unbroken B–L symmetry is an intriguing and testable mechanism to generate the initial conditions of the hot early universe. If B–L is broken at the grand unification scale, the false vacuum phase yields hybrid inflation, ending in tachyonic preheating. The dynamics of the B–L breaking Higgs field and thermal processes produce an abundance of heavy neutrinos whose decays generate entropy, baryon asymmetry and gravitino dark matter. We study the phase transition for the full supersymmetric Abelian Higgs model. For the subsequent reheating process we give a detailed time-resolved description of all particle abundances. The competition of cosmic expansion and entropy production leads to an intermediate period of constant ‘reheating’ temperature, during which baryon asymmetry and dark matter are produced. Consistency of hybrid inflation, leptogenesis and gravitino dark matter implies relations between neutrino parameters and superparticle masses. In particular, for a gluino mass of 1 TeV, we find a lower bound on the gravitino mass of 10 GeV.

Variety ofSO(10)GUTs with natural doublet-triplet splitting via the missing partner mechanism

We present a new class of unified $SO(10)$ models where the grand unified theory symmetry breaking down to the standard model gauge group involves just one scale, in contrast to the conventional $SO(10)$ models which require two scales. Further, the models we discuss possess a natural doublet-triplet splitting via the missing partner mechanism without fine-tuning. Such models involve $560+\overline{560}$ pair of heavy Higgs fields along with a set of light fields. The $560+\overline{560}$ are the simplest representations of $SO(10)$ besides the $126+\overline{126}$ which contain an excess of color triplets over $SU(2{)}_{L}$ doublets. We discuss several possibilities for realizing the missing partner mechanism within these schemes. With the $126+\overline{126}$ multiplets, three viable models are found with additional fields belonging to ${210+2\ifmmode\times\else\texttimes\fi{}10+120}$, ${45+10+120}$, or ${210+16+\overline{16}+10+120}$. With the $560+\overline{560}$, a unique possibility arises for the missing partner mechanism, with additional ${2\ifmmode\times\else\texttimes\fi{}10+320}$ fields. These models are developed in some detail. It is shown that fully realistic fermion masses can arise in some cases, while others can be made realistic by addition of vectorlike representations. Naturally large neutrino mixing angles, including sizable ${\ensuremath{\theta}}_{13}$, can emerge in these models. The couplings of the ${H}_{u}({H}_{d})$ Higgs doublets of the minimal supersymmetric standard model which give masses to the up quarks (down quarks and leptons) are not necessarily equal at the grand unification scale and would lead to a new phenomenology at the low-energy scales.

NMSSM Higgs benchmarks near 125 GeV

The recent LHC indications of a SM-like Higgs boson near 125 GeV are consistent not only with the Standard Model (SM) but also with Supersymmetry (SUSY). However naturalness arguments disfavour the Minimal Supersymmetric Standard Model (MSSM). We consider the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with a SM-like Higgs boson near 125 GeV involving relatively light stops and gluinos below 1 TeV in order to satisfy naturalness requirements. We are careful to ensure that the chosen values of couplings do not become non-perturbative below the grand unification (GUT) scale, although we also examine how these limits may be extended by the addition of extra matter to the NMSSM at the two-loop level. We then propose four sets of benchmark points corresponding to the SM-like Higgs boson being the lightest or the second lightest Higgs state in the NMSSM or the NMSSM-with-extra-matter. With the aid of these benchmark points we discuss how the NMSSM Higgs boson near 125 GeV may be distinguished from the SM Higgs boson in future LHC searches.

Search for a light neutralino of cosmological interest at the CERN LHC

We address the problem of a search at the LHC for a neutralino whose mass is around 10 GeV, i.e. in the range of interest for present data of direct search for dark matter particles in the galactic halo. This light neutralino is here implemented in an effective Minimal Supersymmetric extension of the Standard Model at the electroweak scale without requirement of a gaugino mass unification at a grand unification scale. In this model, light neutralinos that have the right cosmological properties and are able to explain current results of direct dark matter detection naturally arise. Within this model we identify a specific benchmark which maximizes chances of detection at the LHC, and we determine its prospects of reconstructing the main features of the light neutralino framework at different stages of the LHC runs. Our main result is that the LHC will hardly properly reconstruct the mass of such a light neutralino, due to the intrinsic difficulty in reconstructing the mass of light stable particles in relativistic events. However, the associated measurement of the mass of the heavier neutralinos allows us to point toward the right pattern of gaugino nonuniversality. Other relevant parameters of this model, like slepton and squark masses, can be reconstructed to a good level of precision.